European research on materials known as photonic crystals has made important progress in the race to build all-optical chips for computers and communications systems. The scientists developed a relatively inexpensive way to make high-quality photonic crystals, and showed how these can be integrated into conventional silicon chips.
Photonic crystals are materials whose optical properties vary in a regular, repeating way on a scale of a few hundred nanometres. An ideal photonic crystal can be designed to transmit light of one particular wavelength, and to block all other wavelengths. This gives photonic crystals some very useful properties.
The simplest material of this kind has a layered structure, like a film of oil on water. ‘One-dimensional’ structures like this are used as mirrors, non-reflective coatings, and paints whose colours change with the viewing angle. The gemstone opal, with its shimmering colour, is a natural photonic crystal.
The PHAT project worked with more complex structures whose optical properties vary in two and three dimensions (2D and 3D). Two-dimensional photonic crystals can act as waveguides, channelling light to where it is needed, and as filters to separate different wavelengths – a valuable property in optical communications. Three-dimensional photonic crystals can even trap light within their structures, potentially allowing them to act as optical switches.Shrinking silicon
Communications technology has been revolutionised by electro-optical devices based on the semiconductors gallium arsenide (GaAs) and indium phosphide (InP), optical fibres, and even all-optical amplifiers. But as PHAT spokesperson Gudrun Kocher points out, these devices tend to be much larger than the components needed to make computer chips. GaAs and InP are also expensive materials, and integrating them with silicon brings extra complexities. As a result, she says, most researchers agree that it will be 10-15 years before we see all-optical chips based on conventional (silicon) technology.
This is where photonic crystals come in. A combination of 3D photonic crystal optical switches and 2D waveguides could yield devices that are 10 or even 100 times smaller than those made at the moment. These could be used to assemble all-optical chips made entirely from silicon.Mix and pour
Beads of plastic (PMMA) or silica, 250-900 nm in diameter, are first mixed with water to form a colloidal suspension. Then a solid surface is drawn slowly out of the water, and the beads stick to it in a regular lattice structure. The PHAT team assembled their ‘artificial opals’ by allowing capillary forces to draw the beads along microscopic channels cut in sheets of silicon or silica. In a single dip, they were able to form layers up to 10 mm long and more than 10 beads deep – the minimum practical thickness for a 3D photonic crystal.
The resulting structure of beads separated by air is known as a ‘direct opal’. The resulting refractive index is too low for many applications, so a subcontractor in St. Petersburg used chemical vapour deposition (CVD) to fill the empty spaces with silicon, after which the beads themselves are removed, leaving holes.
A further task was to use electron beam lithography to create a defect layer in the 3D crystals. “That’s because if the crystal is perfect, there’s no way to get light into or out of it,” Kocher explains. Finally, the plan is to sandwich two 3D crystals around a 2D crystal to act as a waveguide.
PHAT was coordinated at the Tyndall National Institute in Cork, Ireland, and had four other partners: the French Atomic Energy Commission (CEA) and University of Montpellier II, Mainz University, Germany, and the Technical Research Centre of Finland (VTT). “This was an ambitious project, and we didn’t manage everything that we set out to do,” says Kocher.
But by the time the project ended, in February 2007, it had two really big achievements under its belt. “We had developed a spatially-selective method of growing photonic crystals, and we had managed to integrate 3D photonic crystals with waveguides, which was a first,” says Kocher.
The crystal fabrication method was patented by two of the project partners, Tyndall and VTT. “This was a significant advance in photonic crystals, and it brings us a step closer to a practical optical computer, ” concludes Kocher.
Christian Nielsen | alfa
Interactive software tool makes complex mold design simple
16.08.2018 | Institute of Science and Technology Austria
Fraunhofer HHI develops next-generation quantum communications technology in the UNIQORN project
16.08.2018 | Fraunhofer-Institut für Nachrichtentechnik, Heinrich-Hertz-Institut, HHI
Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.
Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...
Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur
What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...
08.08.2018 | Event News
27.07.2018 | Event News
25.07.2018 | Event News
16.08.2018 | Life Sciences
16.08.2018 | Earth Sciences
16.08.2018 | Life Sciences